books.google.es - Dirichlet (1805-1859) is well known for his significant contributions to several branches of mathematics. In number theory, for instance, he proved the conjecture by Gauss that there are infinitely many primes in any arithmetic progression such that the first term and the relative difference are relatively...http://books.google.es/books/about/G_Lejeune_Dirichlet_s_Werke.html?id=r6Lwt-5J-psC&utm_source=gb-gplus-shareG. Lejeune Dirichlet's Werke